1. Field of the Invention
The present invention relates to magnetic heads used for writing data on a recording medium and a method of manufacturing the magnetic heads, and to a magnetic head substructure used for manufacturing the magnetic heads.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction perpendicular to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
In each of the longitudinal magnetic recording system and the perpendicular magnetic recording system, magnetic heads typically used have a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate.
In each of the longitudinal and perpendicular magnetic recording systems, the write head comprises a coil for generating a magnetic field corresponding to data to be written on a recording medium, and a magnetic pole layer for allowing a magnetic flux corresponding to the field generated by the coil to pass therethrough and generating a write magnetic field for writing the data on the recording medium. The pole layer incorporates a track width defining portion and a wide portion, for example. The track width defining portion has an end located in a medium facing surface that faces toward the recording medium. The wide portion is coupled to the other end of the track width defining portion and has a width greater than the width of the track width defining portion. The track width defining portion has a nearly uniform width.
To achieve higher recording density, it is a reduction in track width, that is, a reduction in width of the end face of the pole layer taken in the medium facing surface, and an improvement in writing characteristics that is required for the write head. An improvement in writing characteristics is, for example, an improvement in overwrite property that is a parameter indicating an overwriting capability. The overwrite property becomes poorer if the track width is reduced. It is therefore required to achieve a better overwrite property as the track width is reduced. Here, the length of the track width defining portion taken in the direction orthogonal to the medium facing surface is called a neck height. The smaller the neck height, the better is the overwrite property.
A magnetic head used for a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the above-mentioned medium facing surface. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider slightly flies over the surface of the recording medium by means of the airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt called a skew of the magnetic head is created with respect to the tangent of the circular track, in accordance with the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system that exhibits a better capability of writing on a recording medium than the longitudinal magnetic recording system, in particular, if the above-mentioned skew is created, there arise problems, such as a phenomenon in which data stored on an adjacent track is erased when data is written on a specific track (that is hereinafter called adjacent track erasing) or unwanted writing is performed between adjacent two tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing between adjacent two tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
A technique is known for preventing the problems resulting from the skew as described above, as disclosed in U.S. Patent Application Publication No. US 2003/0151850 A1 and U.S. Pat. No. 6,504,675 B1, for example. According to this technique, the end face of the track width defining portion located in the medium facing surface is made to have a shape in which the side located backward in the direction of travel of the recording medium (that is, the side located closer to the air inflow end of the slider) is shorter than the opposite side. Typically, in the medium facing surface of a magnetic head, the end further from the substrate is located forward in the direction of travel of the recording medium (that is, located closer to the air outflow end of the slider). Therefore, the above-mentioned shape of the end face of the track width defining portion located in the medium facing surface is such a shape that the side closer to the substrate is shorter than the side further from the substrate.
As a magnetic head for the perpendicular magnetic recording system, a magnetic head comprising a pole layer and a shield is known, as disclosed in U.S. Pat. No. 4,656,546, for example. In the medium facing surface of this magnetic head, an end face of the shield is located forward of an end face of the pole layer along the direction of travel of the recording medium with a specific small space. Such a magnetic head will be hereinafter called a shield-type head. In the shield-type head, the shield prevents a magnetic flux from reaching the recording medium, the flux being generated from the end face of the pole layer and extending in directions except the direction perpendicular to the surface of the recording medium. The shield-type head achieves a further improvement in linear recording density.
In the course of manufacturing magnetic heads, a number of magnetic head elements to be the magnetic heads are formed in a single substrate (wafer). The substrate in which the magnetic head elements are formed is cut such that the surface to be the medium facing surfaces appears. This surface is then polished to form the medium facing surfaces.
U.S. Pat. No. 5,742,995 discloses a technique in which a first triangle and a second triangle disposed to be opposite to each other are formed in a wafer and these triangles are used to calculate the height of an MR sensor (that is, the length of the MR sensor taken in the direction orthogonal to the medium facing surface). In this technique, the height of the MR sensor is calculated by using the width of the base of the first triangle in the medium facing surface before the wafer is processed (before the wafer is polished), the width of the top of the second triangle in the medium facing surface before the wafer is processed, the width of the base of the first triangle in the medium facing surface after the wafer is polished, and the width of the top of the second triangle in the medium facing surface after the wafer is polished.
Consideration will now be given to a method of forming a pole layer in which the end face of the track width defining portion located in the medium facing surface has a shape in which the side closer to the substrate is shorter than the side further from the substrate, as previously mentioned. In prior art, frame plating has been often employed as a method of forming such a pole layer. According to the method of forming the pole layer by frame plating, an electrode film is first formed on a layer serving as a base of the pole layer. Next, a photoresist layer is formed on the electrode film. The photoresist layer is then patterned to form a frame having a groove whose shape corresponds to the pole layer. Next, plating is performed by feeding a current to the electrode film to form the pole layer in the groove. The frame is then removed. Next, portions of the electrode film except the portion below the pole layer are removed.
When frame plating is employed, it is difficult to form a groove having a small width in the photoresist layer by photolithography. Therefore, the problem is that it is difficult to reduce the track width when the pole layer is formed by frame plating. To solve this problem, it is possible that, after forming the pole layer by frame plating, both side portions of the track width defining portion are etched by dry etching such as ion beam etching so as to reduce the track width.
FIG. 38 illustrates an example of shape of the top surface of the pole layer when the track width is reduced by etching both side portions of the track width defining portion as described above. FIG. 38 shows a neighborhood of the boundary between a track width defining portion 201 and a wide portion 202 of the pole layer before the medium facing surface is formed. In FIG. 38, ‘ABS’ indicates an imaginary surface located in a target location of the medium facing surface that is the location at which the medium facing surface is to be formed, ‘TW’ indicates the track width, and ‘NH’ indicates the neck height as designed.
When the track width TW is reduced by etching the side portions of the track width defining portion 201, it is likely that the pole layer goes out of a desired shape. As a result, particularly when the neck height NH is small, it is likely that the track width defining portion 201 forms a shape in which the width varies depending on the location along the direction orthogonal to the medium facing surface (the vertical direction in FIG. 38), as shown in FIG. 38.
When the track width defining portion 201 has a shape as shown in FIG. 38, the neck height is strictly the length between the imaginary surface ABS and the point at which the width of the track width defining portion 201 starts to be greater than the width thereof taken in the imaginary surface ABS. However, if the neck height is thus defined, it is difficult to precisely determine the neck height when the track width defining portion 201 has the shape as shown in FIG. 38. Therefore, the neck height is defined as will be described below when the track width defining portion 201 has the shape as shown in FIG. 38. In the top surface of the pole layer, an imaginary straight line L1 passes through the intersection point of the imaginary surface ABS and the side portion of the track width defining portion 201, and extends in the direction orthogonal to the imaginary surface ABS. An imaginary straight line L2 extends from a straight line portion of the side portion of the wide portion 202 connected to the side portion of the portion 201 and extends in the direction in which the straight line portion extends. The intersection point of the imaginary straight lines L1 and L2 is defined as C. The distance between the imaginary surface ABS and the point C is defined as the neck height. The neck height as thus defined is nearly equal to the neck height NH as designed.
When the track width defining portion 201 has the shape as shown in FIG. 38, if the location of the medium facing surface goes out of a desired location and the neck height then goes out of a desired value, there is a possibility that the track width TW is out of a desired value, too.
An example of method of manufacturing magnetic heads will now be described. First, components of a plurality of magnetic heads are formed in a single substrate to fabricate a magnetic head substructure in which a plurality of rows of pre-head portions that will be the magnetic heads later are aligned. Next, the magnetic head substructure is cut to fabricate a head aggregate including a single row of the pre-head portions. Next, a surface formed in the head aggregate by cutting the magnetic head substructure is polished (lapped) to form the medium facing surfaces of the pre-head portions that the head aggregate includes. Next, flying rails are formed in the medium facing surfaces. Next, the head aggregate is cut so that the pre-head portions are separated from one another, and the magnetic heads are thereby formed.
An example of method of forming the medium facing surfaces by lapping the head aggregate will now be described. In the method, the head aggregate is lapped so that the MR heights of a plurality of pre-head portions are made equal while the resistances of a plurality of MR elements that the head aggregate includes are detected. The MR height is the length of each of the MR elements taken in the direction orthogonal to the medium facing surface.
According to the method of forming the medium facing surfaces as described above, it is possible to form the medium facing surfaces so that the MR heights are of a desired value. As a result, according to the method, a portion of each medium facing surface at which an end of the MR element is exposed is placed at a desired location. Furthermore, if the angle formed between the medium facing surface and the top surface of the substrate is 90 degrees, a portion of the medium facing surface at which an end face of the track width defining portion is exposed is placed at a desired location, too. As a result, the neck height is of a desired value, too.
In prior art, however, the angle formed between the medium facing surface and the top surface of the substrate is other than 90 degrees in some cases. This is caused by misalignment of the head aggregate and a jig with respect to each other, the jig supporting the head aggregate when the aggregate is lapped. If the angle formed between the medium facing surface and the top surface of the substrate is other than 90 degrees, the portion of the medium facing surface at which the end face of the track width defining portion is exposed is placed at a location deviating from the desired location even though the portion of the medium facing surface at which the end of the MR element is exposed is placed at the desired location. As a result, the neck height is of a value other than the desired value. In FIG. 38, the range indicated with numeral 203 shows a range of deviation from a desired location of the portion of the medium facing surface at which the end face of the track width defining portion is exposed.
As described above, if the neck height is of a value other than the desired value, the track width is of a value other than the desired value, too. As thus described, in prior art the problem is that there are some cases in which the portion of the medium facing surface at which the end face of the track width defining portion is exposed is placed at a location other than the desired location, and the track width is of a value other than the desired value. As a result, the yield of magnetic heads is reduced.
According to the technique disclosed in U.S. Pat. No. 5,742,995, it is possible to calculate the MR height but it is impossible to solve the above-mentioned problem. In addition, it is impossible to detect the target location of the medium facing surface through this technique. Furthermore, according to this technique, it is required to measure the width of the base of the first triangle and the width of the top of the second triangle in the medium facing surface before the wafer is processed (before the wafer is polished), which results in an increase in the number of steps for manufacturing the magnetic heads.